Showing papers by "George M. Whitesides published in 1984"

Lipase-catalyzed hydrolysis as a route to esters of chiral epoxy alcohols

Abstract: equation implies absolute stereochemistry only for l) . The structure of R4 is indicated for each compound in Figure L The substi tuents are hydrogens unless indicated otherwise. We are interested in this reaction partly because it offers a practical synthetic route to certain members of a useful class of chiral substances and partly because it provides an opportunity to compare the characteristics of enantioselective biological and abiological synthetic methods. An init ial survey of enzymesT'8 that hydrolyze glycidol esters indicated that l ipase (E.C. 3.1.1.3, Sigma Type II , from porcine pancreas) has the best combination of act ivi ty, select ivi ty, and cost.e Racemic esters of several epoxy alcohols and related substances were subjected to hydrolysis using this l ipase.l0 To faci l i tate comparison, most reactions were carr ied to 607o complet ion (based on the quanti ty of acid released) under the same condit ions (pH 7.8, T = 25 oC). Unhydrolyzed ester was recovered by extraction (recoveries ranged 60-90Vo of the amount estimated to be present based on acid released). Enantiomeric excesses of recovered ester were measured using Eu(hfc)tr (Figure l ) . These data provide the basis for several observations bearing on the utility of this method. Lipase is not deactivated by reaction

Method of making chiral epoxy alcohols

Abstract: Racemic carboxylic acid esters of epoxy alcohols are enantio selectively hydrolyzed with hydrolytic enzymes to provide chiral epoxy alcohol and chiral unhydrolyzed ester.

The mechanism of hydrogenolysis of dineopentylbis(triethylphosphine)platinum(II)

Abstract: Le complexe du titre reagit avec l'hydrogene a 32°C dans les solvants hydrocarbones et donne du neopentane et du trans-dihydruro (triethylphosphine) platine (II). L'addition du triethylphosphine modifie l'etape limitant la vitesse de la reaction

Chapter 26. Enzymic Methods in Organic Synthesis

Abstract: Publisher Summary This chapter discusses the procedures that use partially or highly purified enzymes to catalyze organic reactions potentially useful in medicinal chemistry. A widespread interest in asymmetric synthesis has focused attention on the demonstrated utility of enzymic catalysis in producing chiral fragments. In fact, the major hindrance to the widespread use of enzymic catalysis is the residual unfamiliarity of many classically trained synthetic chemists in the techniques of enzyme isolation, manipulation, and assay. More than two thousand enzymes are known and several hundred can be obtained commercially. Given sufficient demand, many enzymes can be produced in quantity by recombinant DNA techniques. Enzymes used in synthetic applications are commonly immobilized in or on insoluble materials because immobilization enhances their stability and allows their recovery and reuse. Enzyme stabilization is a concern before, during, and after immobilization. Immobilization often greatly increases the stability of enzymes. Reasons for this stabilization are not clearly understood. Enzyme deactivation during the immobilization process is often troublesome. Enzymic phosphorylation with coupled in situ adenosine triphosphate (ATP) regeneration has been used to prepare glucose-6-phosphate, sn-glycerol-3-phosphate, creatine-phosphate, and 5-phosphoribosyl-1-pyrophosphate. Nicotinamide cofactor dependent oxidoreductases have been applied in chiral synthesis. Enantioselectivity is often only moderate, but in certain cases excellent results have been obtained. Enzymic synthetic methods will see increased use in research and industry. Immunology, neurobiology, endocrinology, molecular genetics, membrane biology, and plant and insect biology are areas that are becoming more molecular in scope.

Practical enzymic synthesis of adenosine 5'-0-(3-thiotriphosphate) (ATP-.gamma.-S)

Abstract: An enzymatic procedure for the synthesis of adenosine 5'-O-(3-thiotriphosphate) (ATP-r-S) on a 5O-mmol scale from dihydroxyacetone, sodium thiophosphate, ADP, and phosphoenol pyruvate is described. The synthesis uses polyacrylamide gel immobilized glycerokinase coupled to a pymvate kinase catalyzed ATP cofactor regeneration system, and polyacrylamide gel immobilized triosephosphate isomerase, glyceraldehyde 3-phosphate dehydrogenase, and phosphoglycerate kinase coupled to a lactate dehydrogenase catalyzed NAD cofactor regeneration system. The ATP-7-S is purified by adsorption on Dowex 1 and isolated as the sodium or barium salts in -90Vo purity.